Decorative laminates having translucent core sheets

ABSTRACT

Decorative laminates which provide a decorative effect similar to that of marble or synthetic marble are achieved by constructing the core from sheets having a very low opacity. These sheets are prepared from bleached Kraft pulp and do not contain titanium dioxide or other opacifying pigments. The core sheets are saturated with resins such as melamine formaldehyde, polyester or epoxy resin. These saturating resins approximately match the refractive index of the bleached Kraft pulp and provide a translucent effect. Core sheets may be assembled with conventional decor sheets and an abrasion-resistant overlay to provide decorative laminates. Due to the translucent nature of the core, the color of the decor sheets is shown throughout the thickness of the laminate. This results in a uniquely decorative edge.

BACKGROUND OF THE INVENTION

This invention relates to a decorative laminate which provides a uniquedecorative effect. More specifically, the invention relates to alaminate which incorporates unpigmented bleached Kraft core sheetssaturated with a resin which renders the core sheets translucent.

Decorative laminates are well-known in the art. They are commonly usedin making table tops, desk tops, kitchen counters, interior and exteriorwall panels, and other articles for residential, office or commercialuse. Decorative laminates are characterized by their low cost,durability, impact and abrasion resistance, decorative clarity,resistance to heat and light, and resistance to mild chemicals.

Decorative laminates are typically constructed of a plurality of coresheets, one or more decor sheets, and optionally an overlay. Each ofthese sheets is impregnated with a resin, assembled into a book andconsolidated or bonded together under high heat and pressure to providea unitary structure.

The core sheets in conventional laminates are unbleached Kraft papersaturated with a phenolic resin. Conventionally, the core sheets areopaque and in many cases they are the brown color of unbleached Kraft. Adecor sheet is normally placed on top of a book of the core sheets inorder to hide the core and to provide a surface upon which decorativeeffects can be produced by printing and like techniques. In some cases,a decor sheet may also be placed on the bottom of the core sheet.

Recently, there has been an increasing demand for solid surfacingdecorative materials and decorative laminates which mimic the decorativeeffect of marble or synthetic marble such as Corian (a trademark of E.I. DuPont deNemours Company) as provided interesting effects indecorative laminates. One response to this need has been the decorativelaminates described in commonly assigned U.S. Pat. No. 4,888,220 whichdiscloses a laminate formed from a decor sheet comprising bleachedcellulose fibers, titanium dioxide and/or a pearl pigment.

SUMMARY OF THE INVENTION

It has now been found that decorative laminates which provide adecorative effect similar to that of marble or synthetic marble can beachieved by constructing the core from sheets having a very low opacity.These sheets are prepared from bleached Kraft pulp and do not containtitanium dioxide or other opacifying pigments. The core sheets aresaturated with resins such as melamine formaldehyde, polyester or epoxyresin. These saturating resins approximately match the refractive indexof the bleached Kraft pulp and provide a translucent effect.

Core sheets in accordance with the invention can be assembled withconventional decor sheets and an abrasion-resistant overlay to providedecorative laminates. Due to the translucent nature of the core thecolor of the decor sheets is shown throughout the thickness of thelaminate. This results in a uniquely decorative edge.

DETAILED DESCRIPTION

Core sheets in accordance with the invention are prepared from bleachedKraft pulp. The pulp may consist of hardwood, softwood, and mixturesthereof. High alpha cellulose pulp can be added to enhance post-formingproperties. The core sheets are formed in a conventional manner. Anyconventional bleaching process may be used to bleach the pulp includingchlorine and chlorine dioxide bleaching processes. The pulp ispreferably bleached to a brightness greater than 80% and typically about88 to 95%.

The core sheets are saturated with a laminating resin which is capableof imparting a translucent effect to the core. Such resins when curedhave a refractive index of about 1.5 to 1.6 which approximately matchesthe retractive index of bleached Kraft which is typically 1.55. Examplesof such resins include melamine-formaldehyde resin, polyester resin, andepoxy resins. These laminating resins saturate the core sheet and areused in a conventional amount.

It is critical that the core sheets do not contain titanium dioxide,pearl pigment, or other opacifying pigment. The core sheets may be freeof any filler, although fillers having a refractive index which isapproximately equal to that of the laminating resin or bleached fiberscan be used. Such fillers include clay, talc, silica, andflame-retardant fillers such as aluminum trihydrate (ATH). These fillerscan be present in an amount of about 0 to 300% based on the amount offiber.

Additives such as alum, alkali, retention aids, wet strength resins,etc. may also be added to the core furnish to control formation,retention and other physical properties in a known manner.

Because the core is translucent, it is no longer necessary to hide thecore. Consequently, decor sheets can be placed at any location withinthe laminate, thereby increasing the number of design possibilities.Because the core is translucent, diffused transmission of light occurswithin the decorative laminate and the core sheets transmit the color ofthe decor sheets within the laminate.

A decor sheet is placed on the top and bottom of the laminate, thereby,sandwiching the core sheets between a pair of decor sheets. Decor sheetsmay also be incorporated or interleaved among the core sheets in anymanner desired. Typically, a laminate will contain a book ofapproximately 1 to 12 core sheets and one or two decor sheets may beincorporated within this book of core sheets together with a top and thebottom decor sheets.

The core sheets in accordance with the present invention preferably havea basis weight of 30 to 200 pounds per 3,000 square feet and preferably70 to 150 pounds per 3,000 square feet.

The decor sheet used in the invention is typically a sheet of highquality cellulose fiber and fillers impregnated with a thermosettingcondensation resin such as melamine-formaldehyde, polyester or epoxyresins. The decor sheet is preferably a solid uniform color. Optionallyit may be printed with a pattern depending upon the decorative effectwhich is desired. The decor sheet may contain opacifying pigmentsincluding titanium dioxide. Additionally, the decor sheet may containstrengthening aids and formation and retention aids all of which areknown in the art and some of which have been previously mentioned withrespect to the core sheets. The decor sheet may range from about 10 to100 pounds or more per 3,000 square feet. A preferred range is 30 to 100pounds per 3,000 square feet. As previously indicated, decor sheets areknown in the art and can be prepared in a conventional manner. Onemethod for preparing the decor sheets is described in U.S. Pat. No.3,135,643.

The laminate will usually include a protective overlay sheet to providebetter abrasion resistance and good surface appearance. Overlay sheetsare well-known in the art. Examples of overlay sheets can be found inCanadian Patent 990,632 and U.S. Pat. Nos. 3,135,643; 3,445,327;3,525,664; 3,798,117; and 3,975,572. Overlay sheets usually containmineral particles such as silica, alumina, titanium oxide, tin oxide,zirconium oxide and the like. The overlay may be formed from alphacellulose fibers and have a basis weight ranging from approximately 12to 35 pounds per 3,000 square feet. Also useful is a high bleached Kraftpulp or alpha pulp beaten to a Canadian standard freeness of about 500ml.

High pressure laminating techniques can be employed in preparinglaminates from the above-described sheets. Temperatures ranging fromabout 120-180 degrees C. and pressures ranging from about 250 to 1500PSI are normally employed. Depending upon the resin system, thelamination cycle may range from about 3 to 300 minutes.

Decorative laminates in accordance with the invention can range inthickness from about 1/16 to about 3/4 inch.

The invention will illustrate in more detail by the followingnon-limiting example:

EXAMPLE

Six sheets of core stock at 130 lb/3000 ft² and containing 85% bleachedhardwood pulp and 15% bleached softwood pulp are treated with melamineformaldehyde resin to a resin content of 55%. On the top and bottom ofthis stack of core sheets are placed decor sheets at 65 lb./3000 ft²with the same pulp combination plus 50% TiO² based on the pulp weight,and the same resin content as the core sheets. Over the top decor sheetis placed a 20 lb./3000 ft² overlay containing 85% bleached softwood and15% bleached hardwood pulps and treated with 65% melamine formaldehyderesin. All resin has been B staged to 5-7% volatiles. The total stack isthen laminated at 300° F. and 1000 psi for 8 min. and then cooled to100° F. The resulting laminate appears to have the same blue white colorof the decor sheets throughout the entire thickness of the laminate.

Having described the invention in detail and by reference to preferredembodiments thereof, it will be apparent that modifications andvariations are possible without departing from the scope of theinvention defined in the appended claims.

What is claimed is:
 1. A solid color decorative laminate having a unique decorative effect at its edge consisting essentially of top and bottom decor sheets, said top and said bottom decor sheets being opaque and a solid color, and a plurality of translucent core sheets free of opacifying pigments interposed between said top and said bottom decor sheets, said core sheets being formed from bleached Kraft pulp fibers and being impregnated with a laminating resin and consolidated with said decor sheets under heat and pressure to form said laminate, said laminating resin when cured having a refractive index sufficiently approximating the refractive index of said pulp fibers to render said core sheets translucent such that the color of said decor sheets is visibly transmitted throughout the thickness of said core sheets when said laminate is viewed from the edge.
 2. The decorative laminate of claim 1 wherein said core sheets have a basis weight of about 30 to 200 pounds per 3,000 square feet.
 3. The decorative laminate of claim 2 wherein said pulp fibers are hardwood, softwood, or mixtures thereof.
 4. The decorative laminate of claim 1 wherein said core sheets include one or more fillers having a refractive index approximately the same as said laminating resin when cured.
 5. The decorative laminate of claim 1 wherein said decorative laminate additionally includes one or more decor sheets interleaved among said plurality of said core sheets.
 6. The decorative laminate of claim 1 wherein said laminate additionally includes an abrasion-resistant overlay sheet.
 7. The decorative laminate of claim 1 wherein said core sheet is free from titanium dioxide.
 8. The decorative laminate of claim 4 wherein said core sheets contain up to about 300% of said one or more fillers having a refractive index approximately the same as said laminating resin when cured.
 9. The decorative laminate of claim 1 wherein said laminating resin when cured has a refractive index of about 1.5 to 1.6.
 10. The decorative laminate of claim 9 wherein said laminating resin is a melamine-formaldehyde resin.
 11. The decorative laminate of claim 1 wherein said decorative laminate has a thickness of about 1/16 to 3/4 inch.
 12. The decorative laminate of claim 1 wherein said bleached Kraft pulp fibers have a brightness greater than about 80%.
 13. The decorative laminate of claim 12 wherein said brightness is about 88 to 95%. 